This invention relates generally to moulding apparatus for the injection moulding of plastics. More particularly, this invention relates to the mounting of a xe2x80x9cleg manifoldxe2x80x9d in a multi-level stack moulding arrangement.
In designing multi-level, multi-cavity stack moulds, such as 2, 3 or 4 level moulds, consideration must be given to maintaining balanced melt flow. It is often ideal to originate melt flow from a central axis of the mould for each level. This may require a melt flow path which originates at the mould axis, extends radially outwardly through a xe2x80x9cleg manifoldxe2x80x9d to the edge of the mould, crosses a xe2x80x9clevelxe2x80x9d through a crossover nozzle and returns radially inwardly back to the central axis through a further leg manifold displaced longitudinally along the mould axis from the first leg manifold. The number of leg manifolds will depend on the number of mould levels. Typical arrangements where radially inward and outward melt flow paths are present are illustrated in U.S. Pat. No. 5,846,472 (three level) and U.S. Pat. No. 5,458,843 (two and four level).
As injection moulding apparatus are principally made of metal which expands significantly between room temperature and its operating temperature, provision has to be made to accommodate thermal growth/contraction of the leg manifold by amounts on the order of 0.125 inches (approximately 3.3 mm). FIG. 1 schematically illustrates a typical axial cross-section through a xe2x80x9cprior artxe2x80x9d mounting arrangement. A leg manifold 10 is illustrated as providing a fluid conduit between a sprue bushing 12 located on the central axis 14 of the mould and a crossover nozzle housing 16 disposed generally parallel to but radially outwardly of the central axis 14 of the mould. The leg manifold 10 is located on the central axis 14 by a means such as a first manifold insulator 18 having a first locating spigot 20 which engages a socket 22 in the leg manifold 10 across from the sprue bushing 12.
In theory at least, the leg manifold 10 will expand radially outwardly from the mould axis 14. The end of the leg manifold adjacent the crossover nozzle housing 16 is clamped between the crossover nozzle housing 16 and a second manifold insulator 24. The second manifold insulator 24 has a second locating spigot 26. The second locating spigot 26, is received in a slot 28 in an injection plate 30 against which it presses. While, it is intended that longitudinal movement should be accommodated by movement of the second spigot 26 in the slot 28 and sliding movement between the leg manifold 10 and the crossover nozzle housing 16, often this doesn""t occur. Instead the first locating spigot 20 ends up being sheared off in turn pressing the leg manifold 10 toward the sprue bushing 12 and misaligning the sprue bushing 12 in its locator ring 30.
A further disadvantage to the prior art design is that there is no clamping force applied to the sprue bushing end of the leg manifold 10. When xe2x80x9csprue breakxe2x80x9d occurs in the injection moulding cycle during which the injection machine nozzle is disengaged from the sprue bushing 12. The sprue bushing is slidably received in a locating ring 32 and therefore doesn""t xe2x80x9cclampxe2x80x9d the leg manifold 10 against the first manifold insulator 18. Repeated engagement and disengagement of the injection machine nozzle and sprue bushing 12 has a xe2x80x9chammeringxe2x80x9d effect on the leg manifold 10 which eventually causes curvature of the leg manifold away from the sprue bushing.
It is an object of the present invention to provide a mounting arrangement for a leg manifold which better accommodates thermal growth and shrinkage than the above described arrangement.
According to the present invention, a manifold mounting arrangement is provided wherein a leg manifold is fixedly secured at a central location along its length rather than at its sprue bushing and whereby thermally induced length changes are accommodated outwardly from this central location. Additionally, a first end of the leg manifold is clampingly secured between a sprue housing and a manifold insulator to avoid movement of the first end toward the sprue upon a sprue break portion of the injection moulding cycle.
More specifically, a manifold mounting arrangement for a leg manifold of an injection moulding apparatus is provided. The manifold mounting arrangement includes an injection plate, a manifold plate secured to the injection plate and a cavity defined between the manifold plate and the injection plate. The leg manifold, which has first and second opposite ends, is disposed in the cavity. The first end of the leg manifold is located by a first manifold insulator extending between the first end and the manifold plate and by a sprue housing having a flange extending between the leg manifold and the injection plate. The second end of the leg manifold is located by a second manifold insulator extending between the second end and the injection plate and by a crossover nozzle housing having a flange extending between the leg manifold and the manifold plate. The leg manifold has a melt passage extending through it which fluidly communicates at the first end with a sprue passage extending through the sprue housing and at the second end with a crossover nozzle passage extending through the crossover nozzle housing. The leg manifold is further supported along its length between central manifold insulators which extend between the leg manifold and the injection plate and between the leg manifold and the manifold plate. The first and second manifold insulators are positioned to allow longitudinal movement of the first and second ends of the leg manifold relative respectively to the sprue housing and the crossover nozzle housing in response to thermal expansion and contraction of the leg manifold. The central manifold insulators constrain the leg manifold from longitudinal movement to limit such movement to the first and second ends.
The central manifold insulators may be secured by respective securing means extending into the injection and manifold plates and at least some of the central manifold insulators may be provided with projections or recesses which engage corresponding projections or recesses in the like manifold to constrain its longitudinal movement.
The securing means may include a socket extending into the manifold plate and a socket extending into the injection plate for respectively receiving the second and the first manifold insulators.
The securing means may alternatively be threaded fasteners. In a preferred embodiment, the central manifold insulators are disposed about midway along the length of the leg manifold so that normal movement is divided approximately equally between the first and second ends relatively respectively to the sprue housing and the crossover nozzle housing.